Considerable efforts have been made to develop remotely deployable occluding devices which can be used to occlude body passageways without requiring significant surgical intervention. A number of researchers have attempted to develop a safe, reliable device which can be deployed through a catheter to occlude a septal defect, such as atrial and ventricular septal defects in the heart. Many of the same devices are used in connection with occluding patent ductus arteriosis (PDA) defects.
One of the first practical systems for reliably occluding septal defects using a transcatheter approach was developed by Dr. Gladwin S. Das and is described in U.S. Pat. Nos. 5,334,217 and 5,578,045 (the teachings of both of which are incorporated herein by reference). All of the devices designed for minimally invasive septal defect occlusion prior to Das' development were cumbersome and relatively difficult to deploy. Most of them were also mechanically complex, greatly increasing the chance of mechanical failure. The simplicity of the Das design greatly facilitated delivery and reduced the likelihood of any mechanical failure of the device.
Briefly, the Das occluder includes a pair of occluding disks attached to one another. In one embodiment illustrated in that patent, each of the disks comprises a membrane with an elastically deformable frame carried about its periphery. The frame is capable of being collapsed so the device may be delivered through a catheter, but is said to be flexible enough to elastically deploy the membrane upon exiting the catheter. The central portions of the two membranes may be attached to one another to define a central “conjoint disk.”
In deploying the Das device, the frames of the two disks are collapsed and the device is inserted into the distal end of a delivery catheter. The catheter is passed through the septal defect to be occluded and the first of the two disks is urged out of the catheter for elastic deployment. The second disk is then urged out of the distal end of the catheter on the other side of the defect to position the central conjoint disk within the defect to be occluded.
While the Das device has proven to be a remarkable advance over the state of the art, it has become clear that some further refinements may be advantageous. In particular, the Das device can be a little difficult to retract once deployed. The Das patents discuss a system for holding the occluder on the distal end of the delivery device using a tether. This permits an operator to retain hold of the device in the event of an improper deployment so the device does not float free within the patient's heart or vascular system. Unfortunately, though, it has proven relatively difficult to reliably and safely retract an inappropriately deployed device back into the lumen of the delivery catheter. While it may be possible to retract the right occluding disk (the second disk to exit the catheter) by retaining a grip on the frame of that disk, it can be much more difficult to retract the left disk (the first occluding disk to be deployed) back into the catheter.
A number of other researchers have attempted to provide improved occlusion devices which can be delivered through a transcatheter approach. For example, in U.S. Pat. No. 5,741,297, Simon discloses a device which has a series of arms used to stretch two separate pieces of fabric. In addition to the single wire joining both of the membranes, the membranes are bonded directly to one another, with the bond being spaced well inwardly of the frame. (This relationship is perhaps best seen in FIGS. 2 and 3.) Simon does not discuss in any detail how this device would be retracted if improperly deployed.
Shaw et al. propose a system for manufacturing occlusion devices which are based on some of the same concepts underlying the Das occluder. In particular, in U.S. Pat. No. 5,879,366, Shaw et al. utilize a pair of membranes which are deployed utilizing a wire frame (38 and 54). These two membranes are joined together at an “attachment point 70” which is formed by sintering a relatively small disk 48 of a bonding polymer. As best seen in FIG. 6B, this attachment point is spaced well inwardly of the two frames and represents a relatively small portion of the overall surface area of the occlusion device. This can make it more difficult to center the device within the defect. This also appears to make it more difficult to retract the device back into a catheter once the second disk has been deployed.